The invention relates to a device for contactless measurement of a rotational angle of a rotating part that is rotatable via a rotating shaft, in particular a throttle valve seated on a control shaft in internal combustion engines in a manner fixed against relative rotation, of the type defined hereinafter.
A measuring device of this type is distinguished by a relatively small structural volume and is suitable for contactless measurement of rotational angles up to 180.degree.. The measuring device includes a tubular body and operates on an eddy current principle, to which end sensor coils are subjected to a flow of a high-frequency alternating current. The resultant magnetic alternating fields of the coils generate eddy currents on the surface of the tubular body. The greater the surface area of the tubular body penetrated by the magnetic field, the more eddy currents are created. These eddy currents cause a reduction in the alternating current resistance of the sensor coils. Upon a rotational motion of the tubular body, the surface area penetrated by the alternating magnetic fields is altered asymmetrically by electrically nonconductive zones, so that in one sensor coil the alternating current resistance increases, while in the other sensor coil the alternating current resistance decreases. Depending on the number, the sensor coils are disposed in a half or full Wheatstone bridge circuit, so that measurement errors occurring at the same time and acting in the same direction are compensated for. The outset voltage of the half or full bridge is a standard for the measured rotational angle.
In this kind of measuring instrument, it is often quite complicated to connect the measuring instrument structurally with the rotating part in terms of the effort of assembly, because the tubular body must be guided around the coil carrier with radial play.